Incidentally, I went ahead and installed as well as activated CS4 on the Mac Pro desktop without incident. It and the twin install on the PPC G5-Quad desktop have been running fine ever since.
There are two possibilities here:
1.— the copy on the Mac Book laptop got automatically deactivated after several months of inactivity (zero contact with the mother ship since January or so), as the machine was effectively dead to the world since early this year because the HD died; or
2.— Adobe's control over the issue is far more lax and ineffective than we had been led to believe.
I don't know which one applies; but I'm just glad to be up and running without my having to deal with that guy in India.